1. Field of the Invention
The invention is related to the field of de-icing, and in particular, to a system that can provide information to assist airport de-icing operations.
2. Statement of the Problem
During inclement weather, ice forms on airplanes as they wait to take-off. The ice adversely affects the flight performance of the airplanes, and may lead to airplane crashes. To prevent this dangerous ice formation, airport personnel apply de-icing fluid to airplanes waiting to take-off during inclement weather. The de-icing fluid effectively prevents dangerous ice formation for a time period after the treatment—referred to as the holdover time. Thus, the holdover time is the time period between a de-icing treatment and the time when the de-icing treatment becomes ineffective and allows ice to form.
It is critical that an airplane take off during its holdover time. If the airplane takes off during its holdover time, then the de-icing treatment remains effective and prevents dangerous ice formation before take off (after take off, the airplane has other means of controlling ice formation). If the airplane cannot take off during its holdover time, then the de-icing treatment loses its effectiveness before take off, and dangerous ice may form on the airplane before take off. In this case, the airplane should return for a second de-icing treatment. It should be appreciated that the accurate calculation and tracking of the holdover time is crucial to airline safety during inclement weather.
Airport personnel use a table like the one below to manually estimate the holdover time. Airport personnel manually enter the left side of the chart based on a temperature range to arrive at a row in the holdover time section of the chart. Airport personnel manually enter the top of the chart based on current weather conditions to arrive at a column in the holdover time section of the chart. The intersection of the row and column yields the holdover time.
HOLDOVER TIME (MIN)FREEZINGFREEZINGFREEZINGLIGHTMODERATEHEAVYTEMP (F.)FOGDRIZZLERAINSNOWSNOWSNOW≧2711-179-132-511-16 6-11NO21-27 8-147-102-5 8-135-8GUIDE14-20 6-105-9 2-5 6-104-6LINE<145-9NO GUIDELINE4-62-4
The National Weather Service indicates current weather conditions, such as snow, freezing fog, freezing drizzle, or freezing rain. Airport personnel use these indications to manually enter the top of the chart. For snow however, airport personnel must estimate whether the snowfall rate is light, medium, or heavy.
Airport personnel estimate the snowfall rate based on visibility. To assess visibility, various targets are placed at various distances (¼ mile, ½ mile, ¾ mile, 1 mile, and 1 ¼ mile). A trained observer determines the furthest target that they can see to establish a visibility distance. For example, if the furthest target that can be seen is the ¾ mile target, then visibility is ¾ mile.
Airport personnel use a table like the one below to manually estimate the snowfall rate based on the visibility estimate. Airport personnel manually enter the left side of the chart based on whether it is day or night. Airport personnel then branch through the chart based on a temperature range to arrive at a row in the visibility section of the chart. Airport personnel manually enter the top of the visibility section of the chart based on the visibility estimate described above to arrive at a column in the visibility section of the chart. The intersection of the row and column yields the snowfall intensity as light, moderate, or heavy, which is used to enter the top of the table described above.
TEMPVISIBILITY (MILE)DAY/NIGHT(F.)≧1¼1¾½≦¼DAY≦30LIGHTLIGHTLIGHTMODERATEHEAVYDAY>30LIGHTLIGHTMODERATEHEAVYHEAVYNIGHT≦30LIGHTLIGHTMODERATEHEAVYHEAVYNIGHT>30LIGHTMODERATEHEAVYHEAVYHEAVY
There are numerous problems associated with the current technique. One problem is the use of airport personnel to manually determine holdover times. This manual approach is prone to human error. The trained observer could inaccurately assess visibility, or the airport personnel could incorrectly use the tables—either of which could provide an incorrect holdover time. An incorrect holdover time could result in a disastrous attempt by an airplane to take-off with icy wings.
Another problem is the use of various ranges to estimate and characterize the holdover time. Snowfall intensity and temperature only have the resolution of a few ranges. The holdover time itself is expressed in ranges, and for heavy snow, no holdover time is given at all. These ranges do not provide the precise data that is required for highly accurate decision making. In addition, the rough ranges may be open to incorrect interpretations by airport personnel. The use of rough ranges clearly results in vague holdover time estimates. In the worst case, an airplane may take off with icy wings due to a vague estimate. More likely is that an airplane is returned for an unnecessary second de-icing treatment, because the holdover time estimate was too conservative. In this case, the airplane is de-iced again even though the initial de-icing treatment is still effective.
Another problem is the use of visibility to estimate snowfall intensity. The visibility estimate only provides a rough estimate of snowfall as light, moderate, or heavy, and does not provide the resolution required to determine more accurate holdover times. The use of a trained observer to manually estimate visibility is also open to human error. In addition, visibility is different at night than during the day, due to the scattering difference between sunlight and an artificial light source that is used at night. The heavy scattering of sunlight reduces visibility, but the same heavy scattering does not occur with the artificial light source, so a trained observer using an artificial light source at night perceive better visibility than they would during the day given the same snowfall intensity. The result is an inconsistency between visibility assessments at night versus the same assessments during the day. This inconsistency may lead to incorrect holdover time estimates.
Further complicating matters is the fact that various de-icing fluids are typically available for selection and use by airport personnel. The different de-icing fluids have differing costs, with the more effective de-icing fluids costing more. For example, a base de-icing fluid may be diluted with water to form various de-icing mixtures. The mixtures with a high concentration of de-icing fluid are more effective, but they are also more expensive. For each de-icing fluid (or de-icing fluid mixture), there is a corresponding table to provide holdover time estimates.
Airport personnel must manually select the appropriate de-icing fluid to use. The selection of the de-icing fluid is based on the holdover time estimates for the various fluids, and the expected delay for the airplanes between de-icing and take-off. As the de-icing fluids can be relatively expensive, the selection of an overly effective de-icing fluid wastes money, because the airplanes take-off well before the de-icing fluid loses effectiveness, and a cheaper de-icing fluid could have been used. The selection of an ineffective de-icing fluid can have disastrous consequences if ice forms on the airplane before take off.
The selection of de-icing fluids is a complex problem that is exacerbated by the other problems described above. The selection of de-icing fluids is based on holdover time estimates that are fairly vague and open to interpretation as described above. Both the estimate of holdover times and fluid selection are manual, and thus, prone to human error.
Another problem is posed by the fact that inclement weather conditions often change dramatically. Consider an example where the proper de-icing fluid is selected and applied to an airplane to provide a holdover time of 8-13 minutes. Now consider that after the de-icing treatment, snowfall intensity increases dramatically, and because of this change in weather conditions, the holdover time estimate is no longer accurate. The current system has no effective mechanism to handle such changed conditions, and it is possible that the airplane would take off with icy wings based on a holdover time estimate that is no longer accurate given the changed conditions.
In a contrasting example, the snowfall intensity may decrease dramatically after de-icing, but airport delays may prevent the airplane from taking off before the holdover time expires. Because the holdover time expired, the airplane would likely be returned for a second de-icing treatment even though the first de-icing treatment was still effective due to the milder weather conditions. The second de-icing treatment is unnecessary adds unwanted cost and delay to airline travel.